The present invention pertains to the field of channel number display systems utilized in television receivers.
Television receivers which include tuners controlled in response to binary signals representing the channel number of a selected channel typically include a two-digit display for displaying the tens and units digits of the selected channel in response to the binary signals. Often, each digit of the display includes a seven-segment light emitting diode (LED) array. Since the binary signals representing the channel number typically include a group of four binary signals arranged in BCD (binary coded decimal) format for each digit, the display typically includes a decoder for each digit to convert the four binary signals representing the respective digit to seven binary signals for controlling the illumination of the seven segments of the respective array. In addition, the display also typically includes seven driver stages for each digit to translate the levels of the seven binary signals for controlling the illumination of the seven segments of the respective array to levels suitable for light emitting diodes. Thus, a typical channel number display includes two decoders and two sets of drivers.
Multiplexing arrangements for channel number displays are known in which the groups of binary signals representing the tens and units digits of the channel number are alternately processed by a single decoder and a single driver arrangement. Accordingly, only one decoder and one set of drivers is required for the channel number display, thereby effecting a cost and power consumption reduction. Unfortunately, since multiplexing involves the switching of signals, switching transients are generated which may undesirably affect the performance of a television receiver. For example, switching transients may exhibit themselves as spots in the picture produced by a receiver. Further, by way of example, switching transients may cause AGC (automatic gain control) circuits of the type which respond to the peak levels of signals to be erroneously set up, thereby causing gain levels of a receiver's RF and IF stages to be incorrectly controlled. While shielding, waveform shaping to slow down switching transients, and component placement techniques may be employed to minimize undesirable effects of switching transients, such techniques tend to increase the cost of receivers. In addition, where waveform shaping to slow down switching transients are employed, the power dissipation of the multiplexing arrangement tends to be increased.